1. Field of the Invention
The present invention relates to an apparatus for injecting a quantity of liquid sample into a continuously flowing carrier liquid. More particularly, it relates to an apparatus for repetitively injecting a predetermined discrete quantity of sample liquid into a continuously flowing carrier liquid. Such an apparatus is useful as a sample injection system for use with a liquid chromatographic column. In such use, the carrier liquid is referred to as the mobile phase.
2. Discussion of the Prior Art
Liquid chromatographs have traditionally been used as research tools. There is, however, a growing trend to use these instruments as industrial process monitors. In such use, the traditional, manual introduction of sample into the column by means of hypodermic injection through a septum is unacceptable.
Automatic injection systems for liquid chromatographs have been developed for process use. Normally, they consist of a "multi-way" valving system designed to isolate a "slug" of sample in a separate portion of the system, usually a short length of tube connected to one set of valves, and then to switch the valves so that the isolated slug of sample is introduced into the continuously flowing carrier stream. Such systems, however, have poor valve life and are prone to leakage. Furthermore, they require an interruption in the flow of carrier liquid, which causes a number of problems, both in the design of the injection system and in the "up-stream" operation of the carrier liquid system. There is, therefore, the need for a simple, reliable, accurate and durable sample injection system for use in liquid chromatographic applications, particularly one which will operate without interrupting the flow of carrier liquid.